Grooved refractory tube for metallurgical casting, assembly of refractory components and casting installation incorporating such an assembly

ABSTRACT

The present invention relates to a grooved refractory pouring tube for pouring a molten metal between an upper metallurgical vessel and a lower metallurgical vessel, a refractory assembly incorporating such a pouring tube, and a casting installation incorporating such an assembly. This refractory pouring tube forms a portion ( 12 ) of a pouring channel and includes at least a first contact face ( 14 ) capable of bearing against a second contact face ( 11 ) of another refractory component ( 9 ) forming an adjacent portion of the pouring channel and provided with an injection groove ( 17 ) forming, in conjunction with the first contact face ( 14 ), a fluid injection channel at least partially encircling the said channel, the said pouring tube ( 4 ) being arranged to be displaced in a predefined trajectory along which the first contact face ( 14 ) slides and remains in bearing contact against the second contact face ( 11 ), whilst the portion ( 12 ) of the pouring channel formed by the said pouring tube intercepts a determinate part ( 23 ) of the injection groove.

The present invention relates to a grooved refractory component, andmore particularly to a pouring tube, for pouring a molten metal betweenan upper metallurgical vessel and a lower metallurgical vessel, arefractory assembly incorporating such a component, and a castinginstallation incorporating such an assembly.

It is known that the continuous casting of steel calls for the fillingof successive metallurgical vessels, notably a ladle, a tundish andingot moulds, and that during its passage from an upper metallurgicalvessel to a lower metallurgical vessel, the metal must as far aspossible be kept out of all contact with the ambient air.

To this end, a pouring shroud or a submerged entry nozzle made ofrefractory material forms an extension to the pouring orifice of theupper vessel (respectively the ladle or tundish), and enters the bath ofmolten metal present in the lower vessel (respectively the tundish oringot mould), so that the molten metal passes from the ladle to thetundish or from the tundish to the ingot mould without ever beingexposed to the ambient air.

The pouring orifice of the upper vessel incorporates an inner nozzle inrefractory material, which opens below this vessel via a contact surfacedesigned to mate with a contact surface on the pouring shroud orsubmerged entry nozzle, thereby forming a joint face between these twocomponents.

Conventionally, a casting installation also includes means of regulatingthe flow of the molten metal. These means may consist of a stopper rodwhich enters the metal bath of the upper vessel opposite the pouringorifice and whose degree of immersion in the said metal bath determinesthe opening of the said pouring orifice. Alternatively, use may also bemade of a slide valve incorporating a set of refractory plates eachhaving an orifice. These plates are normally located between the innernozzle and the pouring shroud or the submerged entry nozzle. The degreeof alignment of the orifices in adjacent plates determines the flow ofmolten metal.

A continuous casting installation therefore includes numerous assembledrefractory components, the interfaces between which are formed bycontact surfaces that may be planar or non-planar, as indicated forexample in document U.S. Pat. No. 5,984,153.

It is known that the reductions in cross-section which occur along themolten metal pouring channel produce considerable negative pressurewhich can in turn lead to an induction of air. To avoid the penetrationof air through the joint surface between two adjacent refractorycomponents, conventional practice involves injecting an inert fluid,more particularly an inert gas such as argon, into an injection grooveformed in the contract surface of one of the components and whichdelineates, in conjunction with the contact surface of the othercomponent, a gas injection channel which nearly completely encircles themolten metal pouring orifice.

The risks of the metal coming into contact with the ambient air are thuseffectively reduced during its passage from the upper vessel to thelower vessel.

More recently, documents WO 98/17420 and WO 98/1741 have also shown thatthe injection channel can effectively perform the additional function ofallowing the injection of a sealing agent, such as graphite for example,to fill cracks propagating from the pouring orifice in the contactsurface of one of the components, or score marks or scratches orientedin the general direction of movement of one of the components during itsreplacement. The sealing agent, which is conveyed by a carrier fluid,limits damage to the refractory around the cracks and/or score marks orscratches, thereby preventing the induction of air through these. Theinjection channel may be open or closed. In the description whichfollows, the terms injection channel or injection groove will be usedequally to describe a channel or groove intended for the injection of aninert gas alone or a sealing agent in a carrier fluid.

The injection channel is therefore very useful. The applicant has found,however, that in certain cases this channel may itself become clogged,i.e. blocked.

In particular, this phenomenon has been observed in the case where theinjection groove is formed in a surface of a refractory pouring tubebearing against the surface of another refractory component (a pouringtube) intended to be replaced during casting operations. For example,when the injection groove is formed in the lower surface of the innernozzle bearing against the upper surface of a pouring shroud or asubmerged entry nozzle.

Although the invention is clearly not limited to this particular case,for reasons of convenience it will be described in the description whichfollows with reference to an injection groove formed in the lower faceof an inner nozzle bearing against the upper face of a submerged entrynozzle.

Replacement of the submerged entry nozzle can be carried out, in a knownmanner, by positioning a new submerged entry nozzle beside the submergedentry nozzle to be replaced, then simultaneously moving the two nozzles,allowing the new nozzle to displace the worn one and take its placebeneath the inner nozzle.

Prior to each replacement, the tundish pouring orifice is closed off,but it is possible for a certain quantity of molten metal to remain atthe joint surface, at the interface between the pouring orifices of theinner nozzle and the submerged entry nozzle. This metal is drawn intothe joint surface as the nozzle is moved, and accumulates in the inertgas injection groove thereby blocking it, which renders it ineffectiveboth in terms of the admission of ambient air and in terms of thetreatment of cracks and score marks or scratches by means of a sealingagent conveyed by the carrier fluid.

The aim of the present invention is to remedy this shortcoming in asimple and economic manner.

The object of the present invention is therefore a refractory pouringtube forming part of a pouring channel and including at least a firstcontact face capable of bearing against a second contact face of anotherrefractory component forming an adjacent portion of the pouring channeland provided with an injection groove forming, in conjunction with thefirst contact face, a fluid injection channel at least partiallyencircling the said pouring channel, the said pouring tube beingarranged to be displaced in a predefined trajectory along which thefirst contact face slides and remains in bearing contact against thesecond contact face, whilst the portion of the pouring channel formed bythe said pouring tube intercepts a determinate part of the injectiongroove, characterised in that the first contact face incorporates anadditional groove positioned so that, in the pouring position, it islocated in proximity to the determinate part of the groove andcommunicates with this groove at least on either side of thisdeterminate part.

The refractory pouring tube is for example a submerged entry nozzle or apouring shroud. The additional groove formed in the contact face allowsthe injected fluid to bypass the obstructed part of the injectiongroove.

In this way, even if the injection groove is obstructed, the injectedfluid is able to circulate completely around the pouring orifice andform a barrier to the ambient air.

An advantageous characteristic of the invention is that the additionalgroove is formed in the refractory pouring tube which is regularlyreplaced, so that the injection channel is cleared each time thispouring tube is replaced, unlike the situation prevailing in the currentstate of the art where replacement of the refractory pouring tube causesthe injection channel to become obstructed.

It is to be noted that the additional groove cannot be too large; forexample, it cannot completely encircle the pouring orifice (such as inthe tube disclosed in document WO 92/20480), otherwise, the additionalgroove could not serve as a bypass for the injected fluid where a partof the injection groove is obstructed. On the contrary, a grooveencircling completely the pouring orifice would form a shortcut for theinjected fluid, preventing thus the metal from being efficientlyprotected by the injected fluid. Preferably, the additional channel isblind so that the pressure in the injection channel is maintained.

According to a particular characteristic, the additional groove isformed to cover the outlet of a delivery and/or discharge conduit (ifany) of the fluid injection channel. This outlet is thus better able toclear itself in case of obstruction.

Preferably, the additional groove should have a width such that, whenthe groove is at the level of the pouring orifice (for example when thetube is changed), it does not communicate with the injection groove.Thus, if some molten metal remains at the interface between the pouringorifices of the inner nozzle and the submerged entry nozzle, it will notreach the injection groove. Therefore, according to an advantageouscharacteristic of the invention, the additional groove is shorter thanthe minimum width between opposite sections of the injection groove oneither side of the pouring orifice at the level of the pouring orifice.

According to another particular characteristic, the first contact faceincorporates a second groove essentially parallel to the additionalgroove. This second groove may be located, relative to the additionalgroove, on the other side of the pouring channel. The function of thissecond groove, referred to below as the scraper groove, is to scrape thecontact face incorporating the injection groove to clean it of any dirtor extraneous material liable to impair the contact quality between thetwo faces, before the new refractory pouring tube is placed in position.

Advantageously, the scraper groove is symmetrical with the additionalgroove relative to the pouring channel. The two grooves are thereforeinterchangeable, which makes it possible to insert the replacementpouring tube without needing to take into account its direction ofmovement. According to its position relative to the injection groove,each groove performs the function of additional groove or scrapergroove.

The object of the present invention is also an assembly of refractorycomponents forming a pouring channel, a first component of the assemblyincorporating at least a first contact face bearing against a secondcontact face of an adjacent refractory component, with a groove beingprovided in the second contact face to form, in conjunction with thefirst contact face, a fluid injection channel at least partiallyencircling the said pouring channel, characterised in that the firstcomponent is a refractory pouring tube such as that described above.

According to a particular characteristic of this assembly, one orcertain of the refractory components incorporate a delivery conduit and,where appropriate, a discharge conduit for the fluid injection channel.

The object of the present invention is also a casting installationincluding an upper metallurgical vessel and a lower metallurgicalvessel, connected by a pouring channel defined notably by an assembly ofrefractory components as described above, the installation alsoincluding a fluid source connected to the delivery line of the fluidinjection channel.

In a particular embodiment, the casting installation also includes ameans of injecting a sealing agent into the fluid.

In order to better explain the invention, a mode of implementation givenby way of example which does not limit the scope of the invention willbe described below with reference to the attached drawing in which:

FIG. 1 is an axial cross-section of an inner nozzle of a tundish and asubmerged entry nozzle,

FIG. 2 is a view on the underside of the contact face of the innernozzle,

FIG. 3 is an upper view on the contact face of the submerged entrynozzle,

FIG. 4 shows the contact faces of the inner nozzle and the submergedentry nozzle superimposed,

FIG. 5 is a view similar to FIG. 1 showing a slide valve interposedbetween the inner nozzle and the submerged entry nozzle,

FIG. 6 is a view on the underside of the bottom plate of a slide valvesimilar to the view in FIG. 2.

FIG. 1 shows the bottom wall 1 of a tundish, in a region surrounding oneof its pouring orifices 2.

The tundish is fitted with a device 3 for changing the tube 4 whichincludes a mounting plate 5 integral with the bottom wall of thetundish, a guide-rails 6 accommodating the collars 7 of two submergedentry nozzles 4 which are held in proximity to the mounting plate 5, anda cylinder to push the two submerged entry nozzles 4 in the guide-rails6. The pouring orifice 2 of the tundish incorporates an inner nozzle 9in refractory material which passes through the mounting plate 5 and issupported at the lower face of the latter by the contact face 11surrounding the pouring orifice and forming a flat contact surface 11.

The guide-rails 6 holds the two submerged entry nozzles 4 against thecontact face 11 of the inner nozzle at an elevated pressure equivalentto a weight of several tonnes. In FIG. 1, the submerged entry nozzle 4on the right is the one which forms, in conjunction with the innernozzle 9, a portion of the pouring channel 12 for the molten metal. Thenozzle on the left is the one which has just been replaced by moving inthe guide-rails 6 under the action of the cylinder 8.

A stopper rod 10 can be applied against the upper orifice 13 of theinner nozzle to regulate the metal flow or to interrupt pouring, notablyto allow replacement of the submerged entry nozzle.

FIG. 2 illustrates the contact face 11 of the inner nozzle.

The pouring orifice has an elongated cross-section oriented in adirection 16 which is parallel to the guide-rails 6, i.e. the directionin which the submerged entry nozzles are moved when the older of the twonozzles is being replaced.

Around the pouring orifice, the contact face incorporates an injectiongroove 17 in the form of a three-quarter partial circle extending intostraight sections of which the ends 19 are close together but which arenot in communication with each other. One end 19 communicates with theoutlet 20 of a delivery line, or where applicable, a discharge line,formed in the inner nozzle 9. Too much importance should not be attachedto the actual shape of the groove 17. Preferably, its ends 19 must beclose together so that the area not circumscribed by the groove isreduced to a minimum, and relatively close to the edge so that theoutlet of the fluid delivery and, where applicable, discharge line isaccessible. This function is fulfilled by the combination of straightand circular portions.

In FIG. 3, it can be seen that each submerged entry nozzle 4 delineatesa portion 24 of elongated transverse cross-section (in direction 16) ofthe pouring channel, and that its collar 7 is rectangular in shape toenable it to be guided in the guide-rails 6 of the submerged entrynozzle changer 3.

The contact face 14 of each submerged entry nozzle, formed by the upperface (according to the orientation in FIG. 1) of its collar 7, coversthe injection groove 17 of the inner nozzle 9 when the submerged entrynozzle 4 is in the working position, and thus forms an injection channelfor fluid and/or sealing agent to prevent the admission of ambient airinto the pouring channel and/or to prevent damage to the refractorymaterial constituting the inner nozzle around its cracks or score marks25.

When the submerged entry nozzle 4 is replaced, the contact faces 14 ofthe two submerged entry nozzles slide in the direction 14 against thecontact face 11 of the inner nozzle. Maximum friction occurs in areas 21and 22 defined by the dotted lines (in FIG. 2), which correspond to thesections passed over by the pouring orifices of the submerged entrynozzles as they move.

Droplets of molten metal present at the interface between the pouringorifices of the inner nozzle and the submerged entry nozzle are drawninto the area 22 located beside the pouring orifice in the direction ofmovement of the submerged entry nozzles, and accumulate in the injectiongroove, which causes obstruction of a determinate part 23 (marked by athick line) of the said injection groove corresponding to itsintersection with the said area 22.

Two additional grooves 26 and 27 are formed in the contact face 14 ofeach submerged entry nozzle 4, at locations corresponding—when the saidsubmerged entry nozzle is in the pouring position—to the parts of theinjection groove 17 contained within the areas 21 and 22 defined by thedotted lines (in FIG. 2) on the contact face of the inner nozzle, i.e.the regions passed over by the injection orifices of the submerged entrynozzles as they move.

In the example shown, the two additional grooves 26 and 27 are centrallysymmetrical about the centre 28 of the contact face, which is equivalentto the centre of the transverse cross-section of the pouring channel, bythe fact that each submerged entry nozzle can be used in the twopossible positions of engagement of its rectangular collar 7 in theguiderails 6.

In reality, only the additional groove 26 covering the determinate part23 of the injection groove performs the function of clearing theinjection channel.

In effect, when the said determinate part 23 of the injection groove 17is obstructed, following the movement of two submerged entry nozzles,the fluid delivered to the injection channel is able to bypass theobstructed section of the injection groove 17 by circulating through theadditional groove 26 of the submerged entry nozzle, which communicateswith the said injection groove on either side of its obstructed part 23.The fluid is thus able to reach the rest of the injection channel toperform its function of preventing the admission of air and/or treatingcracks and score marks or scratches.

Beyond its circular section covering the determinate part 23 of theinjection groove, the additional groove 26 extends into a straightlength which covers the straight section of the injection groove.

The second additional groove 27, which does not cover the determinatepart 23 of the injection groove, nevertheless performs a scrapingfunction on the contact face 11 of the inner nozzle during the movementof the two submerged entry nozzles.

The slide valve 30 in FIG. 5 is interposed between the inner nozzle 9and the submerged entry nozzle 4 described previously.

This slide valve 30 is composed of a fixed upper plate 31, anintermediate mobile plate 32, and a fixed bottom plate 33.

As explained above, the inner nozzle 9 can incorporate an injectiongroove. In this case, the injection channel is formed with the upperface (relative to FIG. 4) of the fixed upper plate 31.

Other joint planes are formed between the fixed plates 31, 33 and themobile plate 32 of the slide valve. As is known, other injectionchannels can be made in these joint planes to prevent the admission ofair.

A joint surface is present between the lower fixed plate 33 and thesubmerged entry nozzle 4 which poses the same risks of damage as thatdescribed in reference to FIGS. 1 to 4, by the fact that replacements ofthe submerged entry nozzle 4 cause friction and risks of obstruction ofan injection groove 34 formed in the lower face (relative to FIG. 4) ofthe lower fixed plate which in conjunction with the contact face of thesubmerged entry nozzle forms a fluid injection channel.

By reason of this risk, the additional grooves 26 and 27 of a submergedentry nozzle identical to that in FIG. 3 fulfil the same functions withregard to the fixed lower plate as in respect of the inner nozzle inFIG. 1.

Although the additional grooves have been described for submerged entrynozzles with reference to a flat joint surface at the outlet of atundish, it is to be understood that the invention applies to any planaror non-planar interface between two refractory components forming afluid injection channel between them.

With regard to FIG. 6, reference will be made mutatis mutandis to thedescription of FIG. 2, and the reference 34 designates an injectiongroove formed in the lower face (relative to FIG. 5) of the fixed bottomplate.

1. tundish bottom wall

2. pouring orifice

3. tube changing device

4. submerged entry nozzle

5. mounting plate

6. slide

7. tube collar

8. cylinder

9. inner nozzle

10. stopper rod

11. inner nozzle contact face

12. part of the pouring channel

13. upper orifice of the inner nozzle

14. tube contact face

16. direction X

17. injection groove

19. groove ends

20. opening of a delivery line or discharge line, respectively

21. area located ahead of the pouring orifice

22. area located after the pouring orifice

23. determinate part of the injection groove

24. portion of elongated transverse cross-section in direction X of thepouring channel of the submerged entry nozzle

25. cracks, score marks and scratches on the inner nozzle

26. additional groove covering the determinate part of the injectiongroove

27. second additional groove

28. centre of the contact face of the submerged entry nozzle

30. slide valve

31. fixed upper plate

32. mobile intermediate plate

33. fixed bottom plate

34. injection groove formed in the lower face (relative to FIG. 5) ofthe fixed bottom plate

What is claimed is:
 1. A refractory pouring tube comprising an innersurface defining a first portion of a pouring channel and a firstcontact face capable of bearing against a second contact face of asecond refractory component defining an adjacent portion of the pouringchannel and provided with an injection groove capable of forming withthe first contact face an injection channel substantially encircling thepouring channel, the pouring tube adapted to be displaced in apredefined trajectory along which the first contact face slides andremains in bearing contact against the second contact face while thefirst portion of the pouring channel intercepts a determinant part ofthe injection groove, the first contact face comprising an additionalgroove and a second groove, the additional groove located proximate tothe determinate part and communicating with the injection groove atleast on either side of the determinate part, and the second groove isessentially parallel to the additional groove and is located, relativeto the additional groove, on the other side of the pouring channel.
 2. Arefractory pouring tube comprising an inner surface defining a firstportion of a pouring channel and a first contact face capable of bearingagainst a second contact face of a second refractory component definingan adjacent portion of the pouring channel and provided with aninjection groove capable of forming with the first contact face aninjection channel substantially encircling the pouring channel, thepouring tube adapted to be displaced in a predefined trajectory alongwhich the first contact face slides and remains in bearing contactagainst the second contact face while the first portion of the pouringchannel intercepts a determinant part of the injection groove, the firstcontact face comprising an additional groove and a second groove, theadditional groove located proximate to the determinate part andcommunicating with the injection groove at least on either side of thedeterminate part, and the second groove is symmetrical with theadditional groove relative to the pouring channel.
 3. The refractorypouring tube of claim 1, wherein the pouring tube comprises a submergedentry nozzle.
 4. The refractory pouring tube of claim 1, wherein theadditional groove comprises a blind groove.